The objectives of this study are to improve immunocytochemical methodology, to apply it to localize cell bodies of luteinizing hormone-releasing hormone (LHRH) neurons in the hypothalamus of the rat, and to characterize the catecholamine afferents to these cell bodies and their terminals in the median eminence (ME) and organum vasculosum of the lamina terminalis (OVLT). Antibodies of LHRH and the unlabeled antibody enzyme (peroxidase anti-peroxidase or PAP) technique of immunocytochemistry will be employed in a modified pre-study of the same immuno-positive structures. LHRH concentrations in cell bodies will be enhanced by using rats during proestrus, following ovariectomy, or after surgical deafferentation of the hypothalamus. Anterior or complete deafferentation will also be used to eliminate certain monoaminergic inputs from areas of study and thus permit catecholamine neutron localization with antibodies to catecholamine synthesizing enzymes. LHRH antibodies and antibodies to tyrosine hydroxylase (TH), dopamine-Beta-hydroxylase (DBH), or phenylethanolamine-N-methyl transferase (PNMT) will be used in combination on the same tissue section. Using separate substrates giving different colored reaction products for each antigen, the relationship between LHRH neurons and those containing catecholamines will be examined at the light and then at the electron microscope level. Quantification of LHRH by radioimmunoassay and of dopamine (DA) and noradrenaline (NA) by the catechol-O-methyl transferade (COMT) assay will be performed on microdissected hypothalamic areas and on the ME and OVLT. These data will be correlated with the results of the immunocytochemical localization.